This invention relates to digital telecommunications switching network fabrics.
Telecommunications switching network fabrics are the means by which individual telecommunications messages and/or circuit connections are routed from an input of a switching system to an output of such a switching system. The input and/or output can be connected either to another switching system, or to a source/destination of the messages or connections.
Largely as a result of the ubiquitous use of optical fiber transmission systems to interconnect switching systems, the switching of modern switching network fabrics is almost entirely performed in the digital mode. For standard telephone conversations, this switching is largely performed by switching pulse code modulation (PCM) signals through time slot interchange (TSI), and time multiplexed (TMS) switches. For the increasing amount of data traffic, packet switches are required. Such switches take a packet from an input data stream, examine and in general, alter, a header identifying the path that the packet is to take, and route the packet to the output indicated by the packet header. Two of the most common types of data inputs are those in the asynchronous transfer mode (ATM), and those in the Internet Protocol (IP).
A problem of the prior art is that the switching network fabrics are in general designed to handle only one type of input and output stream, and that special conversion equipment where necessary, and multiple switching network fabrics are required when multiple types of input and output streams are encountered. One exception to the above statement is that disclosed in U.S. Pat. No. 5,345,446, which discloses arrangements for converting input/output PCM streams into ATM format, and switching the converted as well as the native ATM inputs to a switching system through a common ATM fabric. This approach requires expensive conversion equipment, and is less efficient if the facilities interconnecting switching systems are largely, or predominantly PCM facilities.
The above problem is solved and an advance is made over the prior art in accordance with invention, wherein the input and output streams of a switching network fabric are performed under the control of, and essentially within, a microprocessor. The program of the microprocessor determines how different types of input streams, such as PCM, ATM, or IP are to be switched, and accesses all necessary internal or external memory to select an output stream, and for the case of packet streams, how to alter the header of each received packet. Advantageously, any mix of different types of input stream protocols can be switched, and where necessary, converted, under the control of a single microprocessor entity. If the traffic on one particular input stream changes from one type of protocol to another, the input stream need not be reconnected to a different switching entity; instead the microprocessor is notified of the new type of protocol for this input stream, and performs its switching accordingly.
In accordance with one aspect of this invention, the microprocessor switching entity performs conversions, e.g., between PCM and ATM, as necessary to meet the requirements of an output transmission facility. Advantageously, no separate equipment and separate routing is required.
In accordance with one preferred embodiment, a RISC communications processor such as the PowerPC(copyright) manufactured by the Motorola Corporation, is used as the microprocessor of the switching network fabric. A three hundred MHZ processor, such as the EC 603e of this type can, for example, handle up to 192 PCM streams each consisting of 32 time slots at a bit rate of 2.048 Mbits per second. The capacity is likely to be less if the microprocessor handles packet as well as PCM traffic. On the other hand, if a PowerPC or equivalent processor, is manufactured with a higher clock rate, such a microprocessor can handle more traffic. In one Application, the Input/Output bandwidth and/or the cache size of the processor may be limiting. Advantageously, today""s technology will support a very substantial size switching network fabric unit (element).
In accordance with one arrangement for creating a larger network, a plurality of microprocessor fabric units have their inputs connected in parallel, but each is connected to a different set of output streams. The output streams in some cases, to transmission facilities, and in other cases, to another microprocessor network fabric unit.
In one embodiment, the microprocessor elements generate a bit stream in an output protocol that is different from the input protocol; the output bit stream can then be further switched by other units.
In accordance with another aspect of Applicants"" invention, groups of circuits, or packets, can be switched using this arrangement. Advantageously, such an arrangement can be used efficiently to implement a facilities switch of a type which switches groups of circuits and which responds not to individual call set-up requests, but to group set-up requests, usually from some operating support system.